This invention relates to a method and apparatus for improving core loss values of grain-oriented silicon steel. More particularly, this invention relates to a method and apparatus for "scribing" a moving steel strip to reduce the domain wall spacing to reduce the core loss values.
Grain-oriented silicon steel in the form of strip is produced typically in cold-rolled form. Grain-oriented silicon steels, because of having low core loss, are used in electrical applications such as laminates for the manufacture of transformer cores. Improvement by way of reduction of core loss values in grain-oriented silicon steels is a function of the degree of grain orientation of the steel. It has been determined that core loss values may be reduced by decreasing the magnetic domain wall spacing of the steel strip. It is known to achieve this by scribing the strip in a direction transverse and substantially normal to the rolling direction. This may be achieved by mechanical scribing arrangements wherein a scribing roll is used or by nonmechanical or noncontact arrangements, such as the use of laser devices. Conventional mechanical scribing practices are not sufficiently rapid to be compatible with typical strip line speeds and, therefore, cannot produce the scribe lines at the selected intervals along the length of the strip. In addition, these practices are difficult to control from the standpoint of the magnitude and uniformity of scribing. Laser practices are also expensive and subject to high maintenance costs.
U.S. Pat. No. 4,500,771, issued Feb. 19, 1985, discloses an apparatus and method of scribing ferromagnetic strip material which includes curving the strip around an axis which is parallel to the direction which it is being translated by pairs of convex and concave rollers and then scribing the curved sheet by laser scribing.
EPO Application 140663A (corresponding to U.S. application Ser. No. 545,080, filed Oct. 24, 1983) discloses a platform rotatable about a central axis on which optical elements, such as mirrors, beam splitters, and/or focussing lenses may be mounted for directing a laser beam to treat a curved and moving electrical steel trip to reduce core loss. The steel strip is curved by pairs of convex and concave rollers.
It is, accordingly, a primary object of the present invention to provide a scribing technique that may be used with both contact and noncontact scribing means wherein the scribing at the required intervals may be achieved at typical silicon steel strip line speeds with control of the scribing operation being possible relative to strip line speeds so that the scribing operation may be controlled to produce scribe lines substantially normal to the strip rolling direction at selected intervals along the length of the strip.
It is also desirable to provide a temporary curvature to the strip during scribing without scratching or otherwise damaging the strip surface or crystal structure which could deteriorate watt losses.
This and other objects of the invention, as well as a more complete understanding thereof, may be obtained from the following description and drawings.